#include <stdio.h>

int main() {
    int a, b, c, d, e = 0;
    scanf("%d", &a);
    int arr[a], count[1000001] = {0};
    
    for (b = 0; b < a; b++) {
        scanf("%d", &arr[b]);
        count[arr[b]]++;
    }
    
    for (b = 0; b < a; b++) {
        if (count[arr[b]] == 1) {
            printf("%d\n", arr[b]);
            e = 1;
            break;
        }
    }
    
    if (!e) {
        printf("None\n");
    }
    
    return 0;
}
